A pressure ulcer (pressure injury) is a localized injury to the skin and/or underlying tissue, usually proximate to a bony prominence, developed as a result of a combination of interface pressure, friction/shear, and environmental factors such as moisture and temperature. These ulcers are most commonly associated with diabetics, spinal cord injuries, coma or bed/wheelchair-bound patients, and people who are unable to feel pain from sustained pressure and/or to relieve the pressure/shear that causes the ulcer. Typically, pressure ulcer injuries are categorized by the following stages of severity:                Stage I: Reddening of intact skin that persists despite applied pressure. Stage I pressure ulcers are often coupled with a temperature and/or stiffness change compared to surrounding skin.        Stage II: Damage to or loss of thickness of the dermis, paired with an open wound (broken epidermis). Stage II pressure ulcers can also include open or intact blistering. Generally these pressure ulcers are relatively shallow.        Stage III: Tissue damage and/or loss is full thickness of the skin, down to and including the subcutaneous tissue. Subcutaneous fat may be visible depending on location, but bone, muscle, or tendon are not visible. Underlying fascia is intact.        Stage IV: Damage is severe enough to expose underlying bone, muscle, or tendon.        Unstageable: Exudate, slough, eschar or other debris obscure or fill the wound bed, preventing proper stage assessment until it is removed.        
Sitting on a hard surface or lying in bed produce increased pressures under bony prominences, such as the ischial tuberosities, that exceed intravenous capillary pressure. The combined effect cuts off vascular flow to the high-pressure area, thereby increasing pressure ulcer injury risk. Shearing between the skin and bone can twist and occlude small blood vessels, further promoting ischemia, as well as potentially causing blisters and skin damage at the surface. Moisture resulting from incontinence and sweat can also cause maceration and weakening of skin and tissue, although reduced temperatures may alleviate some of these issues.
Once formed, pressure ulcers are difficult to treat, and the cost of such care—even for a single pressure ulcer—may approach $70,000. As of the date of this application, the total cost of all pressure ulcer treatment and prevention across all patient groups is estimated to easily exceed $1 billion per year in the United States alone.
Currently, long-term wheelchair users have a choice of several different types of pressure-relief wheelchair cushion that are designed to reduce the user's risk of developing a pressure ulcer. Most often, cushions are categorized by the main material used in their construction. The five most common materials are standard and viscoelastic foams, gels, viscous fluids, and air.
These materials may be combined in a variety of ways to produce the cushion. For example, some air-inflated cushions, such as the Roho® line of cushions use inter-connected air cells, allowing the air to flow freely inside the cushion. Another line of air-inflated cushion, from Vicar® use individually sealed chambers, preventing cross-flow. The Jay Medical® Jay® 2 cushion uses gel-filled chamber with a foam substrate to provide support and pressure relief. The chamber is filled with proprietary Jay Flow™ gel, which has been shown to provide good postural stability. However, many of these commercial cushions cost $300-$450 or more.
A wheelchair cushion that matches or exceeds the performance of commercial cushions at a greatly reduced cost could provide a value driven engineering solution for effective pressure ulcer prevention and treatment. Further, a method to design, fabricate, and construct a pressure-relief wheelchair cushion that combines the performance strengths of the existing, proprietary cushions with the economy of non-proprietary, widely available materials would be welcomed.